Illumination systems for viewing instruments, such as endoscopes, industrial boroscopes, or other types of scopes, are generally well known in the art. Because the sites being viewed or inspected by such scopes, such as anatomical or industrial cavities, are not naturally illuminated, illumination must first be provided before any useful viewing or image acquisition can take place. Accordingly, a wide array of such systems have been used.
Earlier scopes employed open flames, and later, platinum filaments. Today, most endoscopic illumination is provided via fiber optic channels that receive light from an image guide coupled to an external, high-powered light source, such as a halogen or xenon lamp. Although such fiber optic systems tend to suffer from a number of disadvantages, including some light loss during the transmission from the external source to the tip of the scope, gradual discoloration and loss of transmission efficiency over time, and the breaking of fiber strands, these systems continue to be the most commonly employed method of providing illumination to the viewing site. However, in certain applications, the use of light emitting diodes has emerged as an alternative means for doing so, as described in the imaging systems disclosed in U.S. Pat. No. 6,730,019 to Irion and U.S. Pat. No. 6,944,316 Glukhovsky et al.
FIG. 1A illustrates a basic illumination system for a traditional endoscope 10. Generally, an endoscope 10 has a fixed line of sight 12 through an objective lens 14. The endoscopic field view field 16 is covered by an illumination field 18, which is typically generated by a remote source 20 and transmitted via a fiber optic light guide 22. The illumination field 18 is designed to cover the entire view field 16 to ensure uniform image brightness. To this end, the illumination field 18 is typically designed to be radially symmetric about the objective lens 14, with light issuing from evenly distributed fiber optic outlets 24, as is shown in FIG. 1B, or a single annular outlet 26, as illustrated in FIG. 1C.
In order to improve the viewing ability of the user, certain endoscopic systems have been provided that include a variable line of sight. Often referred to as swing prism endoscopes, such as that disclosed in U.S. Pat. No. 3,856,000 to Chikama, or pan-tilt endoscopes, such as that described in U.S. Pat. No. 5,762,603 to Thompson, these devices typically have a pivotable line of sight that can cover a certain scanning range. However, with this pivotable line of sight, it becomes necessary to provide illumination over a much wider range than with a single, fixed viewing direction.
Accordingly, a number of illumination systems have been proposed to accommodate these types of endoscopic systems having variable viewing directions. For example, it has been suggested to use separate illumination reflectors, coupled to the imaging reflector, so as to provide a light field that is generally aligned with the viewing field, such as in the systems disclosed in U.S. Pat. No. 3,880,148 to Kanehira et al. and WIPO Publication No. WO 01/22865 to Ramsbottom. However, while this type of arrangement can accommodate a large viewing range, it cannot be made sufficiently compact for midsize (i.e., 4 mm diameter) to small (1 mm diameter) endoscopes.
Another type of system that has been suggested is the use of fibers that are fanned out at the outlet in order to spread the light over the entire viewing range, such as in the systems described in U.S. Pat. No. 4,697,577 to Forkner and U.S. Pat. No. 6,500,115 to Krattiger et al. However, while these arrangements can be made relatively compact, they can only illuminate a limited swing range.
An additional challenge presented by variable direction of view scopes is that, in addition to changing the viewing elevation, it also desirable to be able to rotate the line of sight azimuthally about the shaft of the endoscope in order to achieve truly complete variable viewing. Often, this is accomplished by rotating the entire endoscope. However, this has the disadvantage that the light guide gets wrapped around the instrument in the process. Likewise, endoscopes, that have a fixed handle and a rotatable shaft, allowing the user to perform an azimuthal scan without having to rotate the entire instrument, have a similar problem.
In order to deal with this problem, it has been suggested to use rotating light posts and fiber optic slip rings, such as is described in U.S. Pat. No. 5,621,830 to Lucey et al. However, in practice, these systems have not proven sufficiently effective to replace the standard solution, which entails leaving slack in the fiber bundle in order to give it some freedom to twist. Other systems have been proposed that employ couplings allowing wide azimuthal scanning ranges, such as that disclosed in Krattiger et al. However, these devices employ a mechanism that prevents rotation beyond a particular scan range so that the user does not inadvertently over-twist and destroy the illumination fibers. This limited rotation restricts viewing freedom by forcing the operator to reset the viewing direction once the end of a particular range has been reached.
When the operator decides to change the viewing direction, the instrument should be able to move directly to any new viewing configuration without mechanical constraints or a need to unwind the mechanism and approach the desired view from the opposite direction. Additionally, with the advent of computer-controlled variable direction-of-view endoscopes, such as that disclosed in U.S. Pat. No. 6,663,559 to Hale et al., it has become possible to execute omniramic frame capture sequences for the purpose of building endoscopic maps. Such capture sequences would be most effective and minimize mechanical wear if they are able to be executed in a single continuous scan with no reciprocating motion.
What is desired, therefore, is a system that employs a fixed illumination system that can accommodate the changing line of sight in a scope with a variable direction of view. What is further desired is a system that is both compact and can illuminate a generally circular band swept out by viewing field that moves in accordance with the moving view vector. What is also desired is an illumination system that permits unlimited and continuous rotation of the scope shaft.